Usage Tips:This analog display wall clock is made of high quality acrylic material with white letters and numbers, perfect for classroom or office. As the clock is ticking, the hands move around the dial, showing the time of day through a different math problem for each hour. It's a unique and creative way to keep track of time. This wall clock is a fun and challenging brain exercise. The black dial looks like a chalk board. Each math equation is painted to look like white chalk. Instead of using Roman numerals or traditional numerals, this wall clock has a different equation on each delimitation. It has to be a very fashionable decoration for the wall, especially for the classroom, office and study, and an perfect gift for your friends or their children. It can improve brain exercise and will help you maintain vitality when you see the clock . It's also the perfect office clock for an engineer, mathematician, or anyone who works with numbers. Name: Wall Clock Material: acrylic Color: Black Power supply: 1 x AA battery (not included). Diameter: approx. 30 cm. Package Contents:1pcs x wall clock Only the above package content, other products are not included. Note: Light shooting and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.